1. Field of the Invention
The invention relates generally to a we pumping system for extracting ground water and more particularly to a pump for extracting ground water from construction excavations so construction operations can be performed in a dry subgrade. Prior to excavation the site to be excavated is surrounded by a plurality of wellpoints (small diameter wells) driven, drilled or jetted into the aquifer underlaying the site. The individual wellpoints are connected to a common collector pipe called a header pipe. Rigid pipes rise to the ground surface (risers) and flexible hoses (swings) connect the risers to the header. A wellpoint pump is connected to the header pipe and in operation creates a vacuum on the header which causes the ground water to enter the wellpoints, flow up the riser, pass through the swings into the header and through the pump to a discharge point off site.
While the nature of aquifers vary greatly, the demands on a wellpoint pump are generally the same. At the beginning of the pumping operation, the water level is at its highest and therefore, the water flow rate to the pump is highest. As pumping continues, the ground water level drops, increasing the suction lift requirement of the pump. As the ground water level approaches its lowest point, air enters the wellpoints and the water flow rate is substantially reduced. A wellpoint pump is required to operate continuously (24 hours a day) under these conditions, and is often operating close to cavitation, i.e., high vacuum in the suction; pumping large volumes of air and low volumes of water to maintain the lower ground water level for long time periods until the excavation and the operations below subgrade are completed. The discharge head requirement on wellpoint pumps is generally low in the range of 10 to 20 feet of water.
The system of the invention uses a single positive displacement rotary pump which replaces a conventional centrifugal pump (water pump) and a vacuum pump (air pump) and eliminates the need for an air-water separator. The pumping system of the invention operates at approximately 1/3 engine speed as compared to full engine speed on systems including a centrifugal pump. Additionally, there are less than one-third the number of parts in the pump system of the invention than in prior art systems. Such results in greater reliability and less maintenance. Also, the pump system of the invention is very efficient due to balanced water/air flow.
While applicant's pumping system was originally designed and configured as a wellpoint pump, this unique pumping system has numerous other applications.
2. Description of the Prior Art
There are various types of known wellpoint pump systems. The pump system most commonly used consists of a prime mover (usually a diesel engine) directly driving a centrifugal pump and a belt driving a vacuum pump. An air-water separator with a plurality of floats and valves located in the pump suction line directs air to the vacuum pump and water to the centrifugal pump. These major components along with their respective cooling and or lubricating devices, reservoirs, drive components and connecting flow lines and valves are usually mounted on a structural steel frame for portability. As is evident, this type of wellpoint pump is mechanically and hydraulically complicated. When considering the major components along with the accessory requirements, these prior art pumping systems contain a large number of parts and require a substantial amount of maintenance when operating continuously at or near cavitation.
In another type of known wellpoint pump system, a single positive displacement pump is used to pump both air and water. This system is disclosed in the sales literature of Thompson Pump and Manufacturing Company of Port Orange, Fla. The pump is mounted for horizontal inlet and horizontal outlet. Thus, it tends to run inefficiently because the flow through the pump is unbalanced. Air flows through the upper portions of the rotor vanes and liquid flows through the lower portions. Moreover, the pump has no provision for recirculation and therefore cannot operate for long periods pumping only air. A pump of this type is shown in U.S. Pat. No. 2,697,402.